We will prospectively study 300 healthy individuals over age 70 in the Albuquerque area. Individuals will be given annual history and physical exams as well as in vitro and in vivo evaluation of cellular immunity. We wish to determine whether depressed cellular immune function in otherwise healthy old people correlates with increased morbidity and mortality. We will also investigate the control of humoral and cellular immune responses in vivo and in vitro by prostaglandins.